The present disclosure relates to nondestructive component inspection and, more particularly, to a nondestructive coating inspection system for prognostics and health management, preventative maintenance, and repair of engine parts.
Hot section turbine components in aircraft and industrial gas turbine engines are protected by thermal barrier coatings (TBCs) that provide thermal insulation against high temperatures, and by environmental barrier coatings (EBCs) that provide resistance to environmental attack such as that due to oxidation, corrosion, and recession. TBCs have been used to protect metallic components, especially those constructed from nickel-based superalloys in the hot section of gas turbine engines, such as turbine blades, vanes, endwalls, air seals, and combustor liners. TBCs allow for higher gas temperature operation by protecting components exposed to high temperature gases from thermally activated damage such as melting, creep, oxidation, corrosion, and cyclic thermo-mechanical fatigue, which results in improved fuel consumption, increased thrust or power generation, reduced emissions, improved reliability, reduced cooling requirements, and reduced cost by extended service life and extended time between maintenance intervals.
Thermal protection is typically provided by a ceramic top coat. Coatings are often multilayered systems that include a thermally insulating and porous ceramic topcoat applied on top of various interface and EBC layers that provide additional environmental protection, as well as bonding to the metal alloy substrate. The EBCs and TBCs are considered to be prime reliant, hence are inspected for proper coverage; otherwise, premature field failure may occur. These components are currently inspected manually by visual or tactile inspection. These inspection techniques may be tedious, time consuming, and imprecise.
Several automated inspection processes have been developed based on rapid exterior heating of the component and infrared imaging. For instance, pulsed thermography, where a very short intense flash of light heats a component, has been used to show thermal conductivity of a coating. Similarly, a periodic external thermal signal may be applied to a component and a phase difference in the thermal response indicates damage. These methods, however, require external heating of the component, which may not allow detection of all the desired imperfections, and currently lack automated image analysis for the determination of imperfections and damage.
Methods based on 2D image analytics in visible light have been developed, but these methods are not suitable, for instance, for shallow spallation or for damage on concave surfaces. Methods based on 3D analytics have been developed, but these methods require high resolution 3D scans, which can be slow, and may not detect imperfections such as cracks, delamination, and incorrect coating thickness.